In modern semiconductor technology, it is customary for terminals placed on a semiconductor wafer to be diverted to other terminals by metal interconnects. This allows or simplifies external connection.
The metal interconnects are applied to the semiconductor wafer in a dedicated plane and consist of coated metal, the metals copper, nickel and gold, in this order, usually being used.
To apply the metal interconnects, the semiconductor wafer is coated with a copper seed layer. Then, a photoresist layer is applied and patterned by means of a photolithographic process, thereby forming a photomask for the subsequent electrolysis process.
The openings, which are formed, are then filled with layers of metal by means of an electrolysis process. After the photoresist layer has been removed and the copper seed layer required for the electrolysis process has been etched, the layer structures for signal distribution are what remain.
It is customary for the upper layer of the layer structures to be a precious metal, such as for example gold, with the result that the surfaces of the layer structures are as far as possible protected from environmental influences. However, the base metals of the layer structure are also accessible at the side faces.
This aspect has proven to be a problem, since oxidation and corrosion processes attack sidewalls of the layer structures, thereby reducing the service life of the layer structures and also the reliability of the circuit as a whole.